Since the early days of powered aviation, aircraft have been from time to time troubled by accumulations of ice on component surfaces of the aircraft such as wings and struts under certain flight conditions. Unchecked, such accumulations can eventually so laden the aircraft with additional weight and so alter the airfoil configuration of the wings as to precipitate an unflyable condition. A search for means to combat the accumulation of ice under flying conditions has been a continuing one and has resulted in three generally universal approaches to removing accumulated ice, a process known generically as deicing.
In one form of deicing, leading edges, that is edges of the aircraft component impinged by the air flowing over the aircraft and having a point at which this airflow stagnates, are heated to loosen adhesive forces between accumulating ice and the aircraft component. Once loosened, this ice is generally blown from the aircraft component by the airstream passing over the aircraft. Two methods of heating leading edges have enjoyed significant popularity: In one approach a heating element is placed in the leading edge zone of the aircraft component either by inclusion in a rubber boot applied over the leading edge or by incorporation into the skin structure of the aircraft component. This heating element, typically powered by electrical energy derived from a generating source driven by one or more of the aircraft engines, is switched on and off to provide heat sufficient to loosen accumulating ice. In very small aircraft powered typically by one or two engines, a sufficient quantity of electrical power may be unavailable for the use of electrical deicing.
In the other heating approach, gasses from one or more compression stages of a turbine engine at elevated temperature are circulated through leading edges of components such as wings and struts in order to effect a thermal deicing or antiicing. Employed in aircraft powered by turbine engines, the use of so-called compressor bleeds or by-pass streams from the aircraft engine turbine can result in reduced fuel economy and a lower turbine power output.
In limited situations a chemical is applied to all or part of the aircraft to depress adhesion of ice to the aircraft or to depress the freezing point of water collecting upon surfaces of the aircraft.
The remaining commonly employed method for deicing is typically termed mechanical deicing. In the principal commercial mechanical deicing means, pneumatic deicing, the leading edge zone of a wing or strut component of an aircraft is covered with a plurality of expandable generally tube-like structures inflatable employing a pressurized fluid, typically air. Upon inflation the tubular structures tend to expand the leading edge profile of the wing or strut and crack ice accumulating thereon for dispersal into the airstream passing over the aircraft component. Typically such tube like structures have been configured to extend substantially parallel to the leading edge of the aircraft component. For airfoils such as wings and stabilizers, these structures may extend the entire span of the airfoil. A plurality of tube-like structures frequently are positioned on a wing or strut typically configured to be parallel the leading edge of the wing or strut as by placement in a chord-wise succession away from the leading edge. The plurality of tubes can provide an ice removal function to the entire leading profile of the airfoil or strut.
Certain aircraft components can be possessed of a variety of leading edge profiles. One classical profile is a so-called blunt or bull nosed, substantially rounded leading edge profile having a substantial radius as a percent of the chord of the leading edge which typifies many older aircraft. Such a blunt profile typically includes a generally smoothly rounded, dome shaped leading edge having a large radius. In other, often used component profiles, the leading edge may assume a reduced bluntness resembling a so-called quadrant wedge, but the profile still includes a substantial rounding of the leading edge of the aircraft component characterized by a substantial radius of curvature as a percent of chord. More recently, so-called wedge or knife-edge leading edges have been utilized. In a wedge or knife-edge leading edge, a pair of essentially flat aircraft component surfaces join at an acute angle having a quite modest rounded surface area characterized by a radius of curvature representing a relatively small percent of the chord of the leading edge.
With such wedge or knife edge leading edge profiles, some significant difficulty can occur in applying conventional pneumatic deicing techniques to the deicing of such leading edges.
The ice collection efficiency is high at the small-radius leading edge characterizing knife-edge profiles and the ice collection efficiency is low aft of such leading edges so that ice accretes in a relatively narrow band along the leading edge. With conventional deicers that include a pair of pneumatic tubes straddling the leading edge, this ice is not subject to desirably great movement with inflation of such straddling deicer tubes. Where a tube of a conventional deicer wraps around a leading knife edge uniformly to be symmetrically positioned with equal width portions on each surface, a tendency also can develop for accumulated ice to be pushed forward along the wing structure as the deicer tubes inflate without cracking or breaking to facilitate removal. A pocket forms thereby between the accumulated ice and the pneumatic deicer whereby further inflation cycles of the pneumatic deicer can fail to remove the ice accumulation.
A pneumatic deicer for knife-edge or wedge leading edge profiles that provides a reliable ice cracking action while tending to avoid movement of accumulated ice forward along the aircraft component upon inflation could find substantial application in deicing particularly wings, stabilizers, struts, and other appendages having such a leading edge profile.